Abstract
Extraction of gas (coalbed methane) produces clean energy and can ensure that coal mines maintain high-efficiency production. The currently available coal seam permeability enhancing technologies and modes have certain application restrictions. Therefore, a novel mode is proposed to promote gas extraction. This mode divides complex coal seams into tectonic regions and nontectonic regions based on geological structures. Then, the characteristics of different regions are matched with the advantages of different hydraulic technologies; thus, pressure relief technologies are proposed for tectonic regions, and fracturing technologies are proposed for nontectonic regions. The permeability of coal seams will be sharply increased without leaving unfractured areas. This mode will promote the effectiveness of gas extraction, shorten the extraction time, and ensure safe and efficient production in coal mines. A field application shows that this mode has a better effect than slotted directional hydraulic fracturing technology (SDHFT). The gas concentration and pure gas flow were increased by 47.1% (up to 24.94%) and 44.6% (up to 6.13 m3/min), respectively, compared to SDHFT over 9 months. The extraction time was reduced by 4 months. This mode reduced the number of times that gas concentration exceeded government standards during coal roadway excavation, and the coal roadway excavation speed was increased by 16% (up to 158 m/month).
Highlights
Coalbed methane is a type of clean energy that has a high calorific value and clean combustion products [1,2,3]
This mode divides complex coal seams into tectonic regions and nontectonic regions based on geological structures
We found that the gas concentration exceeded government standards only during excavation work in the tectonic region, especially around the fault
Summary
Coalbed methane is a type of clean energy that has a high calorific value and clean combustion products [1,2,3]. Some researchers have proposed a series of pressure relief technologies, such as hydraulic flushing technology and hydraulic slotting technology [12,13], to improve the effectiveness of gas extraction in cross-measure boreholes and shorten the extraction time by approximately 20% to 30%. Some new types of fracturing fluid have been proposed [19] The effect of these HFTs is significantly improved compared with the pressure relief technologies mentioned above. For some coal mines with multiple geological structures, HFT is not used for fear of causing accidents These mines use only dense borehole gas extraction technology or pressure relief technology, which results in poor extraction efficiency. The permeability of coal seams will be sharply increased by pressure relief or fracturing methods without leaving unfractured areas The use of this mode will promote gas extraction and ensure that production is safe and efficient in coal mines
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